Bulk polymerization of silicone-containing copolymers

ABSTRACT

Methods for preparing silicone-containing polymers by essentially adiabatic polymerization methods are disclosed. The polymerization system includes free radically polymerizable monomers. The monomers include ethylenically unsaturated silicone-containing monomers and/or mercapto-functional silicones as well as additional free radically polymerizable monomers. The silicone-containing polymers are useful as adhesives or release materials.

FIELD OF THE DISCLOSURE

This disclosure relates to bulk polymerization methods to formsilicone-containing polymers, silicone-containing polymers and articlesprepared from silicone-containing polymers.

BACKGROUND

Silicone-containing copolymers are a class of polymeric materials thathave found a wide variety of uses, including uses such as coatings(including release coatings), adhesives (including pressure sensitiveadhesives), gaskets, tubing, vibration dampening materials and the like.

Many of these silicone-containing copolymers arepolydiorganosiloxane-based copolymers. The unique properties of thesecopolymers are derived mainly from the physical and chemicalcharacteristics of the siloxane bond and the organic substituents.Typically the outstanding properties of polydiorganosiloxane copolymersinclude resistance to ultraviolet light, extremely low glass transitiontemperature, good thermal and oxidative stability, high permeability tomany gases, very low surface energy, low index of refraction, goodhydrophobicity and good dielectric properties.

Traditionally silicone-containing copolymers have been prepared insolution. The dissolved copolymer is then cast or coated and dried. Thesolvents aid in the polymerization by solubilizing the reactants andalso serve to dissipate the heat generated during exothermic reactions.

For a number of reasons, it may be desirable to form polymers withoututilizing solvents or where the use of solvent is minimized.Environmental concerns, such as the release of solvents into theatmosphere and the need to recycle and/or dispose of the solvents afteruse, are prompting efforts to reduce or eliminate solvent use. Shipmentof polymers dissolved in solvent can be difficult and expensive. Also,many common solvents are flammable requiring handling of polymersolutions with added safety precautions.

SUMMARY

Disclosed are methods for preparing silicone-containing polymers underessentially adiabatic polymerization conditions. Such polymerizationscan be carried out without the use of solvent or with a minimum ofsolvent and produce polymers which are useful in a variety ofapplications, including as adhesives and release materials.

In one embodiment, a method is disclosed comprising the steps ofproviding a first reaction mixture, deoxygenating the first reactionmixture, heating the first reaction mixture, allowing the first reactionmixture to polymerize under essentially adiabatic conditions to yield anat least partially polymerized mixture, cooling the at least partiallypolymerized mixture, forming a second reaction mixture by addingadditional components to the at least partially polymerized mixture,deoxygenating the second reaction mixture, heating the second reactionmixture, and allowing the second reaction mixture to polymerize underessentially adiabatic conditions to form a polymer. The first reactionmixture may comprise an ethylenically unsaturated silicone-containingmonomer, at least one additional ethylenically unsaturated monomer, achain transfer agent, and a thermal initiator. The thermal initiator maycomprise a single thermal initiator or may comprise a combination ofdifferent thermal initiators. The second reaction mixture may comprise,in addition to the partially polymerized first reaction mixture, anadditional thermal initiator, a chain transfer agent, and optionally asolvent. The heating steps typically comprise heating of the reactionmixtures to a temperature above the activation temperature of a thermalinitiator present in the reaction mixture

In some embodiments, the ethylenically unsaturated silicone-containingmonomer comprises a silicone macromer with the structureW-(A)_(n)-Si(R⁷)_(3-m)Q_(m), wherein W is a vinyl group, A is a divalentlinking group, n is zero or 1, m is an integer of from 1 to 3, R⁷ ishydrogen, alkyl, aryl, or alkoxy; and Q is a monovalent siloxanepolymeric moiety having a number average molecular weight above about500 and is essentially unreactive under copolymerization conditions.

In other embodiments, a method is disclosed comprising the steps ofproviding a first reaction mixture, deoxygenating the first reactionmixture, heating the first reaction mixture, allowing the first reactionmixture to polymerize under essentially adiabatic conditions to yield anat least partially polymerized mixture, cooling the at least partiallypolymerized mixture, forming a second reaction mixture by addingadditional components to the at least partially polymerized mixture,deoxygenating the second reaction mixture, heating the second reactionmixture, and allowing the second reaction mixture to polymerize underessentially adiabatic conditions to form a polymer. The first reactionmixture may comprise a mercapto-functional silicone, at least oneethylenically unsaturated monomer, and a thermal initiator. The thermalinitiator may comprise a single thermal initiator or may comprise acombination of different thermal initiators. The second reaction mixturemay comprise, in addition to the partially polymerized first reactionmixture, an additional thermal initiator, and optionally a solvent. Theheating steps typically comprise heating of the reaction mixtures to atemperature above the activation temperature of a thermal initiatorpresent in the reaction mixture.

In some embodiments, the mercapto-functional silicone has the structure(R¹)_(3-x)(HSR²)_(x)Si—(OSiR⁵R⁶)_(y)—OSi(R³)_(3-q)(R⁴SH)_(q) whereineach R¹ is independently an alkyl, aryl, alkaryl, alkoxy, alkylamino,hydroxyl, hydrogen, or fluoroalkyl group, each R² is a divalent linkinggroup, each R³ is an alkyl, aryl, alkaryl, alkoxy, alkylamino, hydroxyl,hydrogen, or fluoroalkyl group, each R⁴ is a divalent linking group,each R⁵ is an alkyl, aryl, alkaryl, alkoxy, alkylamino, hydroxyl,fluoroalkyl, hydrogen, or —ZSH, wherein Z is a divalent linking group,each R⁶ is an alkyl, aryl, alkaryl, alkoxy, alkylamino, hydroxyl,fluoroalkyl, hydrogen, or —ZSH, wherein Z is a divalent linking group, xis an integer of 0-3, y is an integer of 10 or greater, and q is aninteger of 0-3.

DETAILED DESCRIPTION

Typically, reactions to prepare silicone-containing copolymers,particularly silicone-containing copolymers which are derived from freeradically polymerizable starting materials, such as ethylenicallyunsaturated silicone-containing materials and mercapto-functionalsilicones, are run in a solvent. One reason for this is that thecompatibility of silicone-containing starting materials with otherreactive materials in the reaction mixture is generally low. This lowcompatibility leads to non-homogenous mixtures and incompletepolymerization reactions. The use of solvents helps to overcome thisdifficulty, especially in bulk reactions.

The use of adiabatic polymerization techniques have been used to preparecopolymers from ethylenically unsaturated starting materials. However,it was unclear whether this technique could be used withsilicone-containing starting materials due to the incompatibility ofsilicone-containing materials with other reactive materials in thereaction mixture. This disclosure provides bulk polymerization methodsfor preparing silicone-containing polymers.

The polymerization techniques of this disclosure provide for thepreparation of a wide range of silicone-containing polymers. Dependentupon the composition of the reaction mixture used to form thesilicone-containing polymers, the polymers may be for example,adhesives, such as pressure sensitive adhesives or release materials.The reaction mixture comprises a free radically polymerizablesilicone-containing moiety, a free radically polymerizable co-monomer, achain transfer agent, and a thermal initiator. In some embodiments thefree radically polymerizable silicone-containing moiety may be anethylenically unsaturated silicone-containing monomer, in otherembodiments the free radically polymerizable silicone-containing moietymay be a mercapto-functional silicone. In still other embodiments thereactive mixture may contain a mixture of ethylenically unsaturatedsilicone-containing monomer and mercapto-functional silicone.

The reaction mixture also contains an additional free radicallypolymerizable monomer or monomers. The nature of the additional monomeralso determines the properties of the formed silicone-containingpolymer.

As used herein “polymer” refers to macromolecular materials having atleast five repeating monomeric units, which may or may not be the same.The term polymer, as used herein, encompasses homopolymers andcopolymers.

As used herein “free radically polymerizable” refers to materials whichpolymerize upon exposure to a free radical. Ethylenically unsaturatedgroups and mercapto groups are examples of free radically polymerizablegroups.

As used herein “ethylenically unsaturated” refers to materials whichcontain at least one terminal carbon-carbon double bond (CH₂═CR—), whereR is H or an alkyl group.

Vinyl groups, allyl groups, acrylate groups, and methacrylate groups areexamples of ethylenically unsaturated groups.

As used herein “silicone-containing” refers to materials and polymerswhich contain siloxane linkages. The terms “silicone” and “siloxane” areused interchangeably and refer to materials or polymers which containthe repeat unit (—O—SiR₂—) where each R is independently an alkyl oraryl group.

As used herein the term “silicone macromers” refers tosilicone-containing macromers. Macromers are macromolecular monomers.

As use herein the term “mercapto-functional silicones” refers tosilicone-containing moieties that contain at least one mercapto group(—SH). The mercapto group is the sulfur analog to the hydroxyl group(—OH) and is sometime also referred to as a thiol group. The mercaptogroup is a free radically polymerizable group.

The term “alkenyl” refers to a monovalent group that is a radical of analkene, which is a hydrocarbon with at least one carbon-carbon doublebond. The alkenyl can be linear, branched, cyclic, or combinationsthereof and typically contains 2 to 20 carbon atoms. In someembodiments, the alkenyl contains 2 to 18, 2 to 12, 2 to 10, 4 to 10, 4to 8, 2 to 8, 2 to 6, or 2 to 4 carbon atoms. Exemplary alkenyl groupsinclude ethenyl, n-propenyl, and n-butenyl.

The term “alkyl” refers to a monovalent group that is a radical of analkane, which is a saturated hydrocarbon. The alkyl can be linear,branched, cyclic, or combinations thereof and typically has 1 to 20carbon atoms. In some embodiments, the alkyl group contains 1 to 18, 1to 12, 1 to 10, 1 to 8, 1 to 6, or 1 to 4 carbon atoms. Examples ofalkyl groups include, but are not limited to, methyl, ethyl, n-propyl,isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, n-hexyl, cyclohexyl,n-heptyl, n-octyl, and ethylhexyl.

The term “alkaryl” refers to an monvalent group which is an alkyl groupsubstituted with at least one aryl group, of the general formula —R—Ar.A benzyl group (—CH₂-Ph) is an example of an alkaryl group.

The term “halo” refers to fluoro, chloro, bromo, or iodo.

The term “haloalkyl” refers to an alkyl having at least one hydrogenatom replaced with a halo. Some haloalkyl groups are fluoroalkyl groups,chloroalkyl groups, and bromoalkyl groups. The term “perfluoroalkyl”refers to an alkyl group in which all hydrogen atoms are replaced byfluorine atoms.

The term “aryl” refers to a monovalent group that is aromatic andcarbocyclic. The aryl can have one to five rings that are connected toor fused to the aromatic ring. The other ring structures can bearomatic, non-aromatic, or combinations thereof. Examples of aryl groupsinclude, but are not limited to, phenyl, biphenyl, terphenyl, anthryl,naphthyl, acenaphthyl, anthraquinonyl, phenanthryl, anthracenyl,pyrenyl, perylenyl, and fluorenyl.

The term “alkylene” refers to a divalent group that is a radical of analkane. The alkylene can be straight-chained, branched, cyclic, orcombinations thereof. The alkylene often has 1 to 20 carbon atoms. Insome embodiments, the alkylene contains 1 to 18, 1 to 12, 1 to 10, 1 to8, 1 to 6, or 1 to 4 carbon atoms. The radical centers of the alkylenecan be on the same carbon atom (i.e., an alkylidene) or on differentcarbon atoms.

The term “heteroalkylene” refers to a divalent group that includes atleast two alkylene groups connected by a thio, oxy, or —NR— where R isalkyl. The heteroalkylene can be linear, branched, cyclic, substitutedwith alkyl groups, or combinations thereof. Some heteroalkylenes arepoloxyyalkylenes where the heteroatom is oxygen such as for example,—CH₂CH₂(OCH₂CH₂)_(n)OCH₂CH₂—.

The term “arylene” refers to a divalent group that is carbocyclic andaromatic. The group has one to five rings that are connected, fused, orcombinations thereof. The other rings can be aromatic, non-aromatic, orcombinations thereof. In some embodiments, the arylene group has up to 5rings, up to 4 rings, up to 3 rings, up to 2 rings, or one aromaticring. For example, the arylene group can be phenylene.

The term “heteroarylene” refers to a divalent group that is carbocyclicand aromatic and contains heteroatoms such as sulfur, oxygen, nitrogenor halogens such as fluorine, chlorine, bromine or iodine.

The term “aralkylene” refers to a divalent group of formula—R^(a)—Ar^(a)— where R^(a) is an alkylene and Ar^(a) is an arylene(i.e., an alkylene is bonded to an arylene).

The term “alkoxy” refers to a monovalent group of formula —OR where R isan alkyl group.

The term “alkylamino” refers to a monovalent group of formula—R^(a)—NR^(b)R^(c) where R^(a) is an alkylene and R^(b) and R^(c) areeach independently hydrogen, an alkyl, or an aryl group.

The term “adhesive” as used herein refers to polymeric compositionsuseful to adhere together two adherends. An example of an adhesive is apressure sensitive adhesive.

Pressure sensitive adhesives are well known to one of ordinary skill inthe art to possess properties including the following: (1) aggressiveand permanent tack, (2) adherence with no more than finger pressure, (3)sufficient ability to hold onto an adherend, and (4) sufficient cohesivestrength to be removed cleanly from the adherend. Materials that havebeen found to function well as pressure sensitive adhesives includepolymers designed and formulated to exhibit the requisite viscoelasticproperties resulting in a desired balance of tack, peel adhesion, andshear holding power.

The term “release materials” as used herein refers to polymericmaterials which may be coated onto a substrate to form a releasesurface. A release surface is defined as one that possesses a lack ofadhesion, which provides an easy release from substrates, particularlyadhesive coated substrates. Examples of release surfaces include releaseliners and low adhesion backsizes (LABs). LABs are typically used onadhesive articles, such as tapes, where an adhesive coating is appliedto one side of a backing and a release material is applied to theopposite side. Thus when the tape is rolled up, the adhesive contactsthe LAB permitting the tape to be unrolled again when used.

The terms “weight %”, “wt %” and “% by weight” are used interchangeablyand refer to the weight of component relative to a total compositionweight. Therefore, if a component has a weight % of 30, that indicatesthere are 30 parts by weight of the component to a total compositionweight of 100 parts by weight.

Acrylate and methacrylate monomers are referred to collectively hereinas “(meth)acrylate” monomers. (Meth)acrylate polymers may be copolymers,optionally in combination with other, non-(meth)acrylate, e.g.,vinyl-unsaturated, monomers.

As defined herein, by “essentially adiabatic” it is meant that the totalof the absolute value of any energy exchanged to or from the batchduring the course of reaction will be less than about 15% of the totalenergy liberated due to reaction for the corresponding amount ofpolymerization that has occurred during the time that polymerization hasoccurred. Essentially adiabatic reactions are exemplified in, forexample, U.S. Pat. No. 5,986,011 (Ellis).

In the methods of this disclosure, free radically polymerizable reactionmixtures are subjected to essentially adiabatic polymerizationconditions. Although one essentially adiabatic reaction may be employed,generally two or more essentially adiabatic reaction cycles aregenerally employed if essentially complete conversion of monomer topolymer is desired. There typically is cooling between the reactioncycles. Cooling of the reaction mixture between reaction cyclestypically is performed to prevent the temperature of the reactionmixture from increasing to a point where the product is unstable. Thisinstability can be manifest by polymer discoloration, polymer oxidation,depolymerization to produce undesirable low molecular weight oligomers,etc. The temperature necessary to avoid instability depends in part onthe monomers being used. To avoid such instability the temperature ofthe reaction mixture is generally kept below about 300° C., or evenbelow about 250° C. The reaction conditions are also typically chosen sothat at the end of the final reaction cycle, the product viscosity issuch that draining from the reaction vessel can be performed (Brookfieldviscosity at draining temperature less than about 500,000 centipoise).

Optionally, a series of one or more essentially adiabatic reactioncycles can be used to provide a syrup of polymer dissolved in monomer,typically in the range of about 40-95 weight % based on total weight ofmonomer(s) and polymer where the unreacted monomer can be optionallystripped from the polymer to provide the final polymer product ratherthan running the reaction to completion.

The method of the present disclosure uses one or more thermal freeradical initiators that under the increasing reaction temperatureprofile from essentially adiabatic reaction conditions, provide freeradicals at a rate such that narrow polymer molecular weightdistribution is obtained. The amount of free radicals generated duringthe increasing temperature profile is controlled by the amounts of eachinitiator used and the temperature decomposition characteristics of theselected initiators. This process is capable of achieving polymermolecular weight distributions essentially the same as or narrower thanisothermal solution polymerization methods.

As has been discussed previously, for example in U.S. Pat. No. 5,986,011(Ellis), when appropriately polymerized, essentially adiabatic bulkfree-radical runaway polymerization in a batch reactor can presentseveral advantages:

1) When adiabatically polymerized, because the reaction equipment is notbeing used to cool the reacting mixture, there is not a significanttemperature gradient at the walls of the reaction equipment. Such atemperature gradient can detrimentally broaden the molecular weightdistribution of the polymer by making high molecular weight product inthe cold boundary layer near the reactor wall, because of thefree-radical reaction kinetics well known to those skilled in the art.For example, such high molecular weight components can degrade thecoating performance of a hot-melt coated adhesive or release material.

2) The reaction equipment utilized according to the method of thepresent disclosure is simple.

3) Because heat transfer requirements during reaction are eliminated,the method of the present disclosure more readily scales up fromlab-scale equipment to large production-scale equipment thantemperature-controlled polymerization methods that rely on availableheat transfer area to control reaction temperature.

4) Continuous polymerization reaction equipment contains various degreesof “backmixing” where there is a residence time distribution of thereacting material in the reaction equipment. Some of the reactingmaterial can remain in the reaction equipment for extended periods oftime to degrade product performance by continued attack by thefree-radical initiator to form cross-linked polymer. Crosslinked gelparticles can degrade product performance, such as the coatingsmoothness of a hot-melt coated adhesive or release material.

5) Depending upon the polymer and reaction conditions, essentiallycomplete conversion of monomer to polymer is possible according to themethod of the present disclosure. Based on specific productrequirements, it may be necessary to react the final 1-15 weight % ofmonomer slowly (over a period of one to several hours) to minimize theformation of low molecular weight components as monomer depletes.Residence times of hours in continuous reaction equipment, such as anextruder, can be economically impractical.

A batch reactor is used in the method of the present disclosure. Byreacting batch wise is meant that the polymerization reaction occurs ina vessel where product is drained at the end of the reaction, notcontinuously while reacting. The raw materials can be charged to thevessel at one time prior to reacting, in steps over time while reacting,or continuously over a time period while reacting, and the reaction isallowed to proceed for the necessary amount of time to achieve, in thiscase, polymer properties including the desired polymerization amount,molecular weight, etc. If necessary, additives can be mixed into thebatch prior to draining. When the processing is complete, the product isdrained from the reaction vessel.

A typical batch reactor for this disclosure will comprise a pressurevessel constructed of material suitable for the polymerization, such asstainless steel which is commonly used for many types of free-radicalpolymerization. Typically, the pressure vessel will have ports forcharging raw materials, removing product, emergency pressure relief,pressurizing the reactor with inert gas, pulling vacuum on the reactorhead space, etc. Typically, the vessel is enclosed partially in a jacketthrough which a heat transfer fluid (such as water) is passed forheating and cooling the contents of the vessel. Typically, the vesselcontains a stirring mechanism such as a motor-driven shaft inserted intothe vessel to which stirring blades are attached. Commercial batchreaction equipment typically is sized in the range of about 10 to about20,000 gallons (37.9 to 75,708 liters), and can be custom-built by theuser or can be purchased from vendors such as Pfaudler-U.S., Inc. ofRochester, N.Y.

Caution should be exercised to ensure that the reaction vessel cancontain the elevated vapor pressure of the reaction mixture, at thetemperatures that will be encountered, particularly if the reactionshould proceed faster or further than desired because of an accidentalovercharge/mischarge of initiator(s). It is also very important toensure the reaction mixture will not decompose at the temperaturesencountered to form gaseous products that could dangerously elevate thevessel pressure. Small-scale adiabatic calorimetric experiments, whichone skilled in the art would be readily capable of performing, can beused to determine the runaway characteristics for particular monomersand initiator mixtures. For example, the Reactive System Screening Tool(RSST) or the Vent Sizing Package (VSP), both available from Fauske andAssociates, Inc. of Burr Ridge, Ill., are devices capable ofinvestigating runaway reaction characteristics and severity.

The essentially adiabatic polymerization reaction is carried out with areaction mixture comprising a free radically polymerizablesilicone-containing moiety, a free radically polymerizable co-monomer, achain transfer agent, and a thermal initiator. The free radicallypolymerizable silicone-containing moiety may be an ethylenicallyunsaturated silicone-containing monomer, a mecapto-functional silicone,or a combination thereof. One thermal initiator may be used or acombination of different thermal initiators may be used.

A wide variety of ethylenically unsaturated silicone-containing monomersmay be used. For example, a number of vinyl-functional silicones arecommercially available. Particularly suitable are silicone-containingmacromers, especially ones with the general formula of Formula 1:W-(A)_(n)-Si(R⁷)_(3-m)Q_(m)  Formula 1where W is a vinyl group, A is a divalent linking group, n is zero or 1,m is an integer of from 1 to 3; R⁷ is hydrogen, lower alkyl (e.g.,methyl, ethyl, or propyl), aryl (e.g., phenyl or substituted phenyl), oralkoxy, and Q is a monovalent siloxane polymeric moiety having a numberaverage molecular weight above about 500 and is essentially unreactiveunder copolymerization conditions.

Such macromers are known and may be prepared by the method disclosed byMilkovich et al., as described in U.S. Pat. Nos. 3,786,116 and3,842,059. The preparation of polydimethylsiloxane macromer andsubsequent copolymerization with vinyl monomers have been described inseveral papers by Y. Yamashita et al., Polymer J. 14, 913 (1982); ACSPolymer Preprints 25 (1), 245 (1984); Makromol. Chem. 185, 9 (1984) andin U.S. Pat. No. 4,693,935 (Mazurek). This method of macromerpreparation involves the anionic polymerization ofhexamethylcyclotrisiloxane monomer to form living polymer of controlledmolecular weight, and termination is achieved via chlorosilane compoundscontaining a polymerizable vinyl group.

Suitable monomers for use in the above-mentioned anionic polymerizationare, in general, diorganocyclosiloxanes of the formula (—Si(R⁷)₂—O—)_(r)where each R⁷ is as previously defined and r is an integer of 3 to 7.Examples of useful cyclic siloxanes include, D₃ where r is equal to 3and each R⁷ is methyl and D₄ where r is equal to 4 and each R⁷ ismethyl. The cyclic siloxanes being hereafter designated D₃ and D₄,respectively. D₃, which is a strained ring structure, is especiallyuseful.

Initiators of the anionic polymerization are chosen such thatmonofunctional living polymer is produced. Suitable initiators includealkali metal hydrocarbons such as alkyl or aryl lithium, sodium, orpotassium compounds containing up to 20 carbon atoms in the alkyl oraryl radical or in some instances up to 8 carbon atoms. Examples of suchcompounds are ethylsodium, propylsodium, phenylsodium, butylpotassium,octylpotassium, methyllithium, ethyllithium, n-butyllithium,sec-butyllithium, tert-butyllithium, phenyllithium, and2-ethylhexyllithium. Lithium compounds are preferred as initiators. Alsosuitable as initiators are alkali metal alkoxides, hydroxides, andamides, as well as triorganosilanolates of the formula R⁸Si(IC)₂—O-Mwhere M is alkali metal, tetraalkylammonium, or tetraalkylphosphoniumcation and where each R⁷, is as previously defined and R⁸ is an alkyl,alkoxy, alkylamino, aryl, hydroxyl or fluoroalkyl. Thetriorganosilanolate initiator lithium trimethylsilanolate (LTMS) isparticularly useful. In general, the use of both strained cyclic monomerand lithium initiator reduces the likelihood of redistribution reactionsand thereby provides siloxane macromonomer of narrow molecular weightdistribution which is reasonably free of unwanted cyclic oligomers.

Molecular weight is determined by the initiator/cyclic monomer ratio,and thus the amount of initiator may vary from about 0.004 to about 0.4mole of organometallic initiator per mole of monomer. Typically, theamount will be from about 0.008 to about 0.04 mole of initiator per moleof monomer.

For the initiation of the anionic polymerization, an inert, generallypolar organic solvent can be utilized. Anionic polymerizationpropagation with lithium counterion typically uses either a strong polarsolvent such as tetrahydrofuran, dimethyl sulfoxide, orhexamethylphosphorous triamide, or a mixture of such polar solvent withnonpolar aliphatic, cycloaliphatic, or aromatic hydrocarbon solvent suchas hexane, heptane, octane, cyclohexane, or toluene. The polar solventserves to “activate” the silanolate ion, making propagation possible.

Generally, the polymerization can be carried out at a temperatureranging from about −50° C. to about 100° C., or from about −20° C. toabout 30° C. Anhydrous conditions and an inert atmosphere such asnitrogen, helium, or argon are usually used.

Termination of the anionic polymerization is, in general, achieved viadirect reaction of the living polymeric anion with halogen-containingtermination agents, i.e., functionalized chlorosilanes, to producevinyl-terminated polymeric monomers. Such terminating agents may berepresented by the general formula W(A)_(n) Si(R⁷)_(3-m)Cl_(m) where Clis a chlorine atom and where W, A, n, m, and R⁷ have been previouslydefined. A preferred terminating agent ismethacryloxypropyldimethylchlorosilane. The termination reaction iscarried out by adding a slight molar excess of the terminating agent(relative to the amount of initiator) to the living polymer at thepolymerization temperature. According to the aforementioned papers by Y.Yamashita et al., the reaction mixture may be ultrasonically irradiatedafter addition of the terminating agent in order to enhancefunctionality of the macromer. Purification of the macromer can beeffected by addition of methanol.

Polymers prepared from these silicone macromers may have a wide varietyor uses. Depending upon the co-monomers used, these polymers may beadhesives, such as pressure sensitive adhesives or they may be releasematerials. Typically the silicone macromer is incorporated into thecopolymer in the amount of about 0.01 to about 50% of the total monomerweight to obtain the desired properties. In some embodiments the amountof silicone macromer is 1-10 weight %, 1-5 weight % or even 3-5 weight%.

In some embodiments the free radically polymerizable moiety may be amercapto-functional silicone. Examples of suitable mercapto-functionalsilicones are described, for example in U.S. Pat. No. 5,032,460 (Kantneret al.). Such mercapto-functional silicones can be represented by thegeneral formula of Formula 2:(R¹)_(3-x)(HSR²)_(x)Si—(OSiR⁵R⁶)_(y)—OSi(R³)_(3-q)(R⁴SH)_(q)  Formula 2

wherein each R¹ is a monovalent moiety which can independently be thesame or different and is selected from the group consisting of alkyl,aryl, alkaryl, alkoxy, alkylamino, hydroxyl, hydrogen, and fluoroalkyl;

each R² can independently be the same or different and is a divalentlinking group;

each R³ is a monovalent moiety which can independently be the same ordifferent and is selected from the group consisting of alkyl, aryl,alkaryl, alkoxy, alkylamino, hydroxyl, hydrogen, and fluoroalkyl;

each R⁴ can independently be the same or different and is a divalentlinking group;

each R⁵ is a monovalent moiety which can independently be the same ordifferent and is selected from the group consisting of alkyl, aryl,alkaryl, alkoxy, alkylamino, hydroxyl, fluoroalkyl, hydrogen, and —ZSH,wherein Z is a divalent linking group;

R⁶ is a monovalent moiety which can independently be the same ordifferent and is selected from the group consisting of alkyl, aryl,alkaryl, alkoxy, alkylamino, hydroxyl, fluoroalkyl, hydrogen, and —ZSH,wherein Z is a divalent linking group;

x is an integer of 0-3;

y is an integer of 10 or greater;

q is an integer of 0-3;

R⁵ comprises 0-y —ZSH moieties;

R⁶ comprises 0-y —ZSH moieties;

wherein at least one of the following is true: q is an integer of atleast 1; x is an integer of at least 1; R₅ comprises at least one —ZSHmoiety; and R₆ comprises at least one —ZSH moiety.

In some embodiments, R¹ comprises either a C₁-C₄ alkyl group or anhydroxyl group. These groups are typically chosen for reasons ofcommercially availability. Especially useful are embodiments where R¹ isa methyl or butyl group.

Typically, the divalent linking group R² comprises a C₁ to C₁₀ alkylene,arylene, alkarylene and alkoxyalkylene group. In some embodiments, R² iseither a C₁-C₃ alkylene or a C₇-C₁₀ alkarylene due to ease of synthesisof these compounds. For reasons of availability, especially useful areembodiments where R² is a —CH₂—; a —CH₂CH₂CH₂—; or a —CH₂—(C₆H₄)—CH₂CH₂—group.

In some embodiments, R³ comprises a either a C₁-C₄ alkyl group or anhydroxyl group. These groups are typically chosen for reasons ofcommercially availability. Especially useful are embodiments where R³ isa methyl or butyl group.

Typically, the divalent linking group R⁴ comprises a C₁ to C₁₀ alkylene,arylene, alkarylene and alkoxyalkylene group. In some embodiments, R⁴ iseither a C₁-C₃ alkylene or a C₇-C₁₀ alkarylene due to ease of synthesisof these compounds. For reasons of availability, especially useful areembodiments where R⁴ is a —CH₂—; a —CH₂CH₂CH₂—; or a —CH₂—(C₆H₄)—CH₂CH₂—group.

Typically, the groups R⁵ and R⁶ independently comprise alkyl, aryl,alkaryl, alkoxy, alkylamino, hydroxyl, fluoroalkyl, hydrogen, or —ZSHgroups, wherein Z is a divalent linking group. Useful divalent linkinggroups Z include, for example, C₁ to C_(m) alkylene, alkarylene,arylene, and alkoxyalkylene groups. Generally, for reasons of commercialavailability, Z is a —CH₂— or a —CH₂CH₂CH₂— group. In embodiments whereR⁵ or R⁶ does not comprise a —ZSH group, they typically comprise a C₁ toC₃ alkyl, a fluoroalkyl, or a phenyl group. Generally, when R⁵ or R⁶does not comprise a —ZSH group, they are methyl groups.

Typically, y is an integer ranging from about 40 to about 270 in orderto provide the silicone segment with a molecular weight ranging fromabout 3,000 to about 20,000 in order to provide suitable releaseperformance. In some embodiments, y is an integer ranging from about 67to about 270 in order to provide the silicone segment with a molecularweight ranging from about 5,000 to about 20,000. In some embodiments thenumber average molecular weight of the mercapto-functional silicone isin the range from 2,000-20,000 grams/mole or from 5,000-10,000grams/mole.

The number of mercapto-functional groups on the mercapto-functionalsilicone compound can vary. The ratio of the weight ofmercapto-functional groups to the total weight of themercapto-functional silicone compound can range from about 0.5:99.5 toabout 15:85. Typically, the weight ratio of mercapto-functional groupsto mercapto-functional silicone compound ranges from about 2:98 to about10:90. In some embodiments the mole % of —CH₂CH₂CH₂SH groups in themercapto-functional silicone ranges from 1-20 mole % or from 2-4 mole %.

Useful mercapto-functional silicone compounds can be prepared by anyknown method including, for example, those presented in U.S. Pat. Nos.4,238,393; 4,046,795; 4,783,490 and Canadian Patent No. 1,233,290. Aparticularly useful mercapto-functional silicone is commerciallyavailable from ShinEtsu Silicones, Akron, Ohio as “KF-2001”.

Typically, the amount of mercapto-functional silicone present in thereactive mixture is in the range of 1-40 weight %, 5-35 weight %, oreven 10-30 weight %.

The free radically polymerizable reaction mixtures of this disclosurealso comprise a free radically polymerizable co-monomer. A wide varietyof free radically polymerizable co-monomers or mixtures of co-monomersmay be used. Examples of suitable monomers include vinyl monomers,(meth)acrylate monomers and polar copolymerizable monomers.

Typically, the polymers formed by the method of this disclosure containat least 50% by weight of co-monomers relative to the total monomercontent. In some instances the polymers contain 60%, 70%, 80% or even90% or more by weight of co-monomers relative to the total monomercontent.

The co-monomers used affect the final properties of the formed polymer,so the proposed use for the polymer will influence the monomerselection. For example, Tg is one polymer parameter that may beimportant in the formed polymer. Typically, when the polymer is to beused as an adhesive, especially a pressure sensitive adhesive, theco-monomers are generally chosen such that the formed polymer has a Tgof less than 20° C. or even less than 0° C. On the other hand, when thepolymer is to be used as a release material, the co-monomers aregenerally chosen such that the formed polymer has a Tg of greater than20° C. or even greater than 30° C.

The substitution and functionality of the co-monomers are also a factorin determining which co-monomers are used. For example, in someembodiments it may be desirable to form a pressure sensitive adhesivepolymer which is free of acidic groups. In this instance when it isdesirable to have polar copolymerizable monomers present in the polymer,acid functional monomers are generally avoided and basic functionalmonomers are used instead.

Examples of suitable vinyl monomers include, for example, vinyl esters(e.g., vinyl acetate), styrene, substituted styrenes (e.g., alpha-methylstyrene), vinyl halides, vinyl propionates, and mixtures thereof. Otheruseful vinyl monomers include macromeric (meth)acrylates such as(meth)acrylate-terminated styrene oligomers and(meth)acrylate-terminated polyethers, such as are described in PCTPatent Application WO 84/03837 and European Patent Application EP140941.

(Meth)acrylate monomers are (meth)acrylate esters of non-tertiary alkylalcohols, the alkyl groups of which comprise from about 1 to about 20,or about 1 to about 18 carbon atoms, such as those of Formula 3:H₂C═CR⁹—C(O)—OR¹⁰  Formula 3

wherein R⁹ is H or CH₃, the latter corresponding to where the(meth)acrylate monomer is a methacrylate monomer, and R¹⁰ is a linear,branched, aromatic, or cyclic hydrocarbon group, and —C(O)— represents acarbonyl group. When R¹⁰ is a hydrocarbon group, it can also includeheteroatoms (e.g., oxygen or sulfur).

Examples of suitable (meth)acrylate monomers useful in the presentdisclosure include, but are not limited to, benzyl methacrylate, n-butylacrylate, n-butyl methacrylate, cyclohexyl acrylate, cyclohexylmethacrylate, decyl acrylate, 2-ethoxy ethyl acrylate, 2-ethoxy ethylmethacrylate, ethyl acrylate, 2-ethylhexyl acrylate, ethyl methacrylate,n-hexadecyl acrylate, n-hexadecyl methacrylate, hexyl acrylate,hydroxy-ethyl methacrylate, hydroxy ethyl acrylate, isoamyl acrylate,isobornyl acrylate, isobornyl methacrylate, isobutyl acrylate, isodecylacrylate, isodecyl methacrylate, isononyl acrylate, isooctyl acrylate,isooctyl methacrylate, isotridecyl acrylate, lauryl acrylate, laurylmethacrylate, 2-methoxy ethyl acrylate, methyl acrylate, methylmethacrylate, 2-methyl butyl acrylate, 4-methyl-2-pentyl acrylate,1-methylcyclohexyl methacrylate, 2-methylcyclohexyl methacrylate,3-methylcyclohexyl methacrylate, 4-methylcyclohexyl methacrylate,octadecyl acrylate, octadecyl methacrylate, n-octyl acrylate, n-octylmethacrylate, 2-phenoxy ethyl methacrylate, 2-phenoxy ethyl acrylate,propyl acrylate, propyl methacrylate, n-tetradecyl acrylate,n-tetradecyl methacrylate, and mixtures thereof.

In some embodiments, particularly release materials, it may be desirableto choose (meth)acrylate co-monomers which as homopolymers have Tggreater than 20° C. or even greater than 30° C. Examples of suitable(meth)acrylate monomers include, but are not limited to, t-butylacrylate, methyl methacrylate, ethyl methacrylate, isopropylmethacrylate, n-butyl methacrylate, isobutyl methacrylate, s-butylmethacrylate, t-butyl methacrylate, stearyl methacrylate, phenylmethacrylate, cyclohexyl methacrylate, isobomyl acrylate, isobornylmethacrylate, benzyl methacrylate, bromoethyl methacrylate,2-hydroxyethyl methacrylate, hydroxypropyl methacrylate, glycidylmethacrylate, allyl methacrylate,

In some embodiments, in which the formed polymers are either adhesivesor release materials, it may be desirable to include copolymerizablepolar monomers. Examples of such polar monomers include: acid functionalmonomers such as acid functional (meth)acrylates; basic functionalmonomers such as (meth)acrylamides, substituted (meth)acrylamides, andamine-containing (meth)acrylates; and neutral polar monomers such ashydroxyalkyl (meth)acrylates, and cyanoalkyl (meth)acrylates.

Useful acidic functional monomers include, but are not limited to, thoseselected from ethylenically unsaturated carboxylic acids, ethylenicallyunsaturated sulfonic acids, ethylenically unsaturated phosphonic acids,and mixtures thereof. Examples of such compounds include those selectedfrom acrylic acid, methacrylic acid, itaconic acid, fumaric acid,crotonic acid, citraconic acid, maleic acid, oleic acid, B-carboxyethylacrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid,2-acrylamido-2-methylpropane sulfonic acid, vinyl phosphonic acid, andthe like, and mixtures thereof. Due to their availability, typicallyethylenically unsaturated carboxylic acids are used.

When acidic (meth)acrylate co-monomers are used, typically they areadded in amounts ranging from about 2% by weight to about 30% by weight,or about 2% by weight to about 15% by weight, relative to the totalmonomer content. Generally, as the proportion of acidic monomers used inpreparing the acidic copolymer increases, cohesive strength of theresulting polymer increases.

A wide variety of basic monomers are useful. In some embodiments, thebasic monomer is a nitrogen-containing monomer, such as those of Formula4:R¹¹R¹²C═CR¹³—X_(a)—Y  Formula 4

wherein

a is 0 or 1;

R¹¹, R¹², and R¹³ are independently selected from H— and CH₃— or otheralkyl group,

X is selected from an ester or amide group; and

Y is an alkyl group, a nitrogen-containing aromatic, nitrogen-containinggroup, such as the group:—(Z)_(b)—NR₁₄R₁₅

wherein

Z is a divalent linking group (typically about 1 to 5 carbon atoms);

b is 0 or 1; and

R¹⁴ and R¹⁵ are selected from hydrogen, alkyl, aryl, cycloalkyl, andalkaryl groups.

R¹⁴ and R¹⁵ in the above group may also form a heterocycle. In allembodiments, Y, R¹¹, and R¹² may also comprise heteroatoms, such as O,S, N, etc. While Formula 4 summarizes the majority of basic monomersuseful in the present disclosure, other nitrogen-containing monomers arepossible if they meet the definition of a basic monomer (i.e., can betitrated with an acid).

Exemplary basic monomers include N,N-dimethylaminopropyl methacrylamide(DMAPMAm); N,N-diethylaminopropyl methacrylamide (DEAPMAm);N,N-dimethylaminoethyl acrylate (DMAEA); N,N-diethylaminoethyl acrylate(DEAEA); N,N-dimethylaminopropyl acrylate (DMAPA);N,N-diethylaminopropyl acrylate (DEAPA); N,N-dimethylaminoethylmethacrylate (DMAEMA); N,N-diethylaminoethyl methacrylate (DEAEMA);N,N-dimethylaminoethyl acrylamide (DMAEAm); N,N-dimethylaminoethylmethacrylamide (DMAEMAm); N,N-diethylaminoethyl acrylamide (DEAEAm);N,N-diethylaminoethyl methacrylamide (DEAEMAm); N,N-dimethylaminoethylvinyl ether (DMAEVE); N,N-diethylaminoethyl vinyl ether (DEAEVE); andmixtures thereof. Other useful basic monomers include vinylpyridine,vinylimidazole, tertiary amino-functionalized styrene (e.g.,4-(N,N-dimethylamino)-styrene (DMAS), 4-(N,N-diethylamino)-styrene(DEAS)), N-vinyl pyrrolidone, N-vinyl caprolactam, acrylonitrile,N-vinyl formamide, (meth)acrylamide, and mixtures thereof.

When basic co-monomers are used, typically they are added in amountsranging from about 2% by weight to about 30% by weight, or about 2% byweight to about 15% by weight, relative to the total monomer content.Generally, as the proportion of basic monomers used in preparing thebasic copolymer increases, cohesive strength of the resulting polymerincreases.

Another useful class of co-monomers which may be included in thereaction mixture are co-monomers that may be described ascopolymerizable initiators. This class of co-monomers comprise a freeradically polymerizable group and an initiator group. The initiatorgroup may be a thermally initiated group or a photoinitiated group.Comonomers which are copolymerizable photoinitiators are particularlysuitable to provide crosslinking. This is particularly true for polymerswhich may be hot melt processed and subsequently crosslinked. This typeof crosslinking, also known as post curing, usually comprises exposingthe coated material to some form of radiant energy, such as electronbeam, or ultraviolet light with the use of a chemical crosslinkingagent. Examples of useful copolymerizable photoinitiators are disclosed,for example, in U.S. Pat. No. 6,369,123 (Stark et al.), U.S. Pat. No.5,407,971 (Everaerts et al.), and U.S. Pat. No. 4,737,559 (Kellen etal.). The copolymerizable photocrosslinking agents either generate freeradicals directly or abstract hydrogen atoms to generate free radicals.Examples of hydrogen abstraction type photocrosslinkers include, forexample, those based on benzophenones, acetophenones, anthraquinones,and the like. Examples of suitable copolymerizable hydrogen abstractioncrosslinking compounds include mono-ethylenically unsaturated aromaticketone monomers free of orthoaromatic hydroxyl groups. Examples ofsuitable free-radical generating copolymerizable crosslinking agentsinclude but are not limited to those selected from the group consistingof 4-acryloxybenzophenone (ABP), para-acryloxyethoxybenophenone, andpara-N-(methacryloxyethyl)-carbamoylethoxybenophenone. Copolymerizableinitiators, when used, are typically included in the amount of about 0%to about 2%, or in the amount of about 0.025% to about 0.5%, based onthe total monomer content.

The reaction mixture also comprises a chain transfer agent. Chaintransfer agents are well known in the polymerization art to control themolecular weight or other polymer properties. The term “chain transferagent” as used herein also includes “telogens”. Suitable chain transferagents include, but are not limited to, those selected from the groupconsisting of carbon tetrabromide, hexanebromoethane,bromotrichloromethane, 2-mercaptoethanol, t-dodecylmercaptan,isooctylthioglycoate, 3-mercapto-1,2-propanediol, cumene, and mixturesthereof. Depending on the reactivity of a particular chain transferagent and the amount of chain transfer desired, typically 0.1 to about 5percent by weight of chain transfer agent is used, or 0.1 to about 1.0percent by weight or even 0.1 to 0.5 percent by weight, based upon thetotal monomer content.

The reaction mixture also comprises at least one thermal initiator.Thermal initiators are species which generate free radicals uponheating. Many possible thermal free radical initiators are known in theart of vinyl monomer polymerization and may be used. Typical thermalfree radical polymerization initiators which are useful herein areorganic peroxides, organic hydroperoxides, and azo-group initiatorswhich produce free radicals. Useful organic peroxides include but arenot limited to compounds such as benzoyl peroxide, di-t-amyl peroxide,t-butyl peroxy benzoate, and di-cumyl peroxide. Useful organichydroperoxides include but are not limited to compounds such as t-amylhydroperoxide and t-butyl hydroperoxide. Useful azo-group initiatorsinclude but are not limited to the VAZO compounds manufactured byDuPont, such as VAZO 52 (2,2′-azobis(2,4-dimethylpentanenitrile)), VAZO64 (2,2′-azobis(2-methylpropanenitrile)), VAZO 67(2,2′-azobis(2-methylbutanenitrile)), and VAZO 88(2,2′-azobis(cyclohexanecarbonitrile)). Additional commerciallyavailable thermal initiators include, for example, LUPERSOL 130(2,5-dimethyl-2,5-Di-(t-butylperoxy)hexyne-3) available from ElfAtochem, Philadelphia, Pa., and LUPEROX 101(2,5-dimethyl-2,5-di-(tert-butylperoxoxy)hexane) available from ArkemaCanada, Inc., Oakville,

When the initiator(s) have been mixed into the monomers, there will be atemperature above which the mixture begins to react substantially (rateof temperature rise typically greater than about 0.1° C./minute foressentially adiabatic conditions). This temperature, which depends onfactors including the monomer(s) being reacted, the relative amounts ofmonomer(s), the particular initiator(s) being used, the amounts ofinitiator(s) used, and the amount of any polymer and/or any solvent inthe reaction mixture, will be defined herein as the “runaway onsettemperature”. As an example, as the amount of an initiator is increased,its runaway onset temperature in the reaction mixture will decrease. Attemperatures below the runaway onset temperature, the amount ofpolymerization proceeding will be practically negligible. At the runawayonset temperature, assuming the absence of reaction inhibitors and thepresence of essentially adiabatic reaction conditions, the free radicalpolymerization begins to proceed at a meaningful rate and thetemperature will start to accelerate upwards, commencing the runawayreaction.

A sufficient amount of initiator(s) typically is used to carry thepolymerization to the desired temperature and conversion. If too muchinitiator(s) is used, an excess of low molecular weight polymer will beproduced thus broadening the molecular weight distribution. Lowmolecular weight components can degrade the polymer product performance.If too little initiator is used, the polymerization will not proceedappreciably and the reaction will either stop or will proceed at animpractical rate. The amount of an individual initiator used depends onfactors including its efficiency, its molecular weight, the molecularweight(s) of the monomer(s), the heat(s) of reaction of the monomer(s),the types and amounts of other initiators included, etc. The totalinitiator amount, that for all initiator(s), typically is used in therange of about 0.0005 weight % to about 0.5 weight % or in the range ofabout 0.001 weight % to about 0.1 weight % based on the total monomercontent.

When more than one initiator is used in the reaction, as the firstinitiator depletes during an essentially adiabatic reaction (with thecorresponding increasing reaction temperature), the second initiator maybe selected such that it is thermally activated when the first initiatoris becoming depleted. That is, as the first initiator is depleting, thereaction has brought the reaction mixture to the runaway onsettemperature for the second initiator in the reaction mixture. An overlapis preferred such that before one initiator completely depletes anotherinitiator activates (reaches its runaway onset temperature). Without anoverlap, the polymerization rate can slow or essentially stop withoutexternal heating to bring the mixture to the runaway onset temperatureof the next initiator in the series. This use of external heatingdefeats one of the benefits of the inventive process by adding thepotential for nonuniform temperature distribution in the reactionmixture due to the external heating. However, polymerization stilloccurs under essentially adiabatic conditions.

Until the temperature increases towards the runaway onset temperaturefor an individual initiator in the batch, the initiator is essentiallydormant, not appreciably decomposing to form free radicals. It willremain dormant until the reaction temperature increases towards itsrunaway onset temperature in the reaction mixture and/or until externalheat is applied.

The succession of one initiator depleting and another reaching itsrunaway onset temperature can continue as the temperature rises forvirtually any number of thermal initiators in the reaction system. Inthe limit, a succession of virtually an infinite number of differentinitiators could be used with nearly complete overlap of the activetemperature ranges between adjacent initiators in the succession tobring about the polymerization and the corresponding adiabatictemperature rise. In this case, the amount of each initiator used wouldneed to be virtually infinitesimally small so as to not detrimentallybroaden the molecular weight distribution.

Practically, to minimize raw material handling requirements, areasonable minimum number of initiators should be used to achieve thedesired amount of adiabatic polymerization and obtain the necessarypolymer properties. Typically, 1 to 5 different initiators (moretypically 2 to 5) are used during a particular reaction cycle. In somecircumstances it may be advantageous to use 2, 3, 4, or 5 differentinitiators per reaction cycle.

To estimate the amount of overlap between successive initiators in aseries during an essentially adiabatic polymerization, standardpolymerization modeling techniques can be employed as described in U.S.Pat. No. 5,986,011 (Ellis).

In the case that there will be more than one reaction cycle, theinitiator(s) for the first essentially adiabatic reaction cycle aretypically selected to bring the reaction to a temperature/conversionlevel where:

1) The polymerization reaction virtually stops when the initiator(s)have essentially depleted (i.e., initiator(s) more than 99% depleted).The temperature of the reaction mixture is such that thermalpolymerization of the monomers (polymerization in the absence of addedfree radical initiators) in the polymer/monomer reaction mixture ispractically negligible. This is important so that the reaction can bestopped with available heat transfer from the reactor jacket (andpotentially augmented with external cooling such as that from externalcooling from pumping the reaction fluid through a heat exchanger, etc.).

2) The solution viscosity is such that when the reaction mixture iscooled prior to the next reaction cycle, the next initiator(s), optionalchain transfer agent, optional additional monomers, optional polymer,etc., can be mixed into the batch. This viscosity will be typically lessthan about 200,000 centipoise (Brookfield viscosity at mixingtemperature) for a common batch reactor system.

Typically the polymerization reactions of this disclosure proceed asfollows. The monomers are charged to the reactor in the desired amounts.The temperature of the reaction vessel must be cool enough so thatvirtually no thermal polymerization of the monomers will occur and alsocool enough so that virtually no polymerization will occur when theinitiator(s) are added to the batch. Also, care should be taken toensure the reactor is dry, in particular, free of any undesired volatilesolvent (such as reactor cleaning solvent) which potentially coulddangerously elevate the pressure of the reaction vessel as thetemperature increases due to heat of polymerization. The initiator(s),chain transfer agents, and optional additional materials are alsocharged to the reactor.

Prior to warming the reaction mixture as described below (or optionallysimultaneously while warming the batch), after adding all components tothe batch as described above, the batch is purged of oxygen, afree-radical polymerization inhibitor. De-oxygenation procedures arewell known to those skilled in the art of free-radical polymerization.For example, de-oxygenation can be accomplished by bubbling an inert gassuch as nitrogen through the batch to displace dissolved oxygen.

After completing the de-oxygenation, the head space in the reactor istypically pressurized with an inert gas such as nitrogen to a levelnecessary to suppress boiling of the reaction mixture as the temperaturerises during reaction. The inert gas pressure also prevents oxygen fromentering the polymerization mixture through possible small leaks in thereaction equipment while polymerization is in progress.

From heating provided by the jacket on the reactor, the reaction mixturetemperature typically is raised to or in a range about 1° C. to about 5°C. above the runaway onset temperature with sufficient mixing in thebatch to have an essentially uniform temperature in the batch. The batchtemperature controller is typically set temporarily to maintain thebatch at the runaway onset temperature. Once the jacket temperaturebegins to drop as necessary to hold the batch at the runaway onsettemperature, this indicates that the polymerization has begun. Thereaction may not proceed immediately when the batch is brought to therunaway onset temperature because it may take time to deplete reactioninhibitors that are typically shipped with the monomer (to preventunwanted polymerization during shipping and handling), other traceimpurities, or any oxygen still dissolved in the reaction mixture. Assoon as the jacket temperature drops, the reactor jacket temperaturecontrol system is set to track the batch temperature as it increases,due to reaction, to facilitate essentially adiabatic reactionconditions. In practice, it has been found beneficial to have the jackettrack about 1° C. to about 10° C. above the batch to warm the reactorwalls from the jacket as opposed to warming the reactor walls from theheat of reaction of the mixture, making the reacting system moreadiabatic. Acknowledged is the fact that perfect adiabiticity isprobably not attainable because there will typically be a small amountof heat transferred from the reacting medium to the internal agitatorblades and shaft as well as the mixing baffles in the reactor. Inpractice, the effect of heat loss to heating the agitator shaft andblades, baffles, temperature probes, etc., has been found to benegligible.

An alternate heating approach would be to gently warm the batch past therunaway onset temperature with heat input from the jacket to warm thebatch at a rate of about 0.1° C./min to about 0.5° C./min and continuethe heating through the reaction cycle (similar to the heating approachabove with the jacket tracking about 1° C. to about 10° C. above thebatch temperature). As in the heating approach above, continued heatingthrough the reaction cycle would serve to offset the heat loss to thereaction equipment and maintain essentially adiabatic reactionconditions. In practice, the first heating approach described aboveappears preferable because it ensures the reaction will always commenceat the same temperature which seems to produce more reproducible productfrom batch to batch.

Once the reaction temperature has peaked, due to the depletion of thethermal initiator(s) as well as negligible reaction of the monomers fromthermal polymerization, the polymer content at this point is typicallyabout 30-80% by weight based on the total weight of monomer(s) andpolymer.

If desired, the polymerization cycles can be stopped at this point andthe unreacted monomer stripped from the reaction mixture or furtherpolymerized in other equipment. Stripping apparatuses for the purpose ofremoving residual monomer are well known to those skilled inpolymerization art. One potential stripping apparatus is anextractor-extruder operating with sections vented to vacuum chamberswherein the monomer can be condensed and optionally reused in subsequentpolymerizations. Typical extractor-extruders are referred to in ModernPlastics Encyclopedia, Volume 45, October 1968 and Volume 46, October1969, both published by McGraw-Hill.

A potential benefit of stopping the polymerization without reacting tocompletion is that the molecular weight distribution has been found tobroaden as conversion increases towards completion. Product propertyrequirements could warrant the extra effort and cost of stripping versusreacting to completion. Another reason to cease the polymerizationprocess at partial conversion would be to limit the solution viscosityat manageable levels. For example, as the polymer molecular weightincreases, the solution viscosity will increase. If high molecularweight polymer is to be produced and the 100% conversion melt viscosityis not manageable, i.e. greater than about 200,000 to about 500,000centipoise (Brookfield viscosity at temperature), stopping the reactionat less than 100% conversion could be beneficial.

When the reaction system is to be further polymerized in one or moreessentially adiabatic reaction cycles, the batch temperature typicallyis cooled prior to beginning the next reaction cycle. Generally thebatch is cooled about 5-20° C. below the runway onset temperature of theinitiator used in the next reaction cycle. If more than one initiator isused the batch temperature is typically cooled at least about 5-20° C.below the runaway onset temperature of the initiator having the lowestrunaway onset temperature.

As the partially polymerized reaction mixture cools, its viscosity willincrease. Optionally, if necessary, additional monomer(s) can be addedto the batch before it has fully cooled to compensate for the increasingviscosity. Typically, if necessary, a relatively small amount will beadded. Charging additional monomer in the amount less than about 30weight % of the amount of monomer added in the first reaction cycle ispreferred. While the batch is cooling or when it has cooled to thedesired temperature, optionally more monomer(s) can be added to adjustmonomer ratios to compensate for unequal reactivity ratios of themonomers in the previous reaction cycle. Similarly, monomer(s) notincluded in an earlier reaction cycle can be added to tailor the polymerproperties as needed. Monomer addition may also be performed as anin-process correction to compensate for slight batch-to-batch variationsin the amount of reaction conversion obtained in a previous reactioncycle.

When the batch has cooled to the desired temperature, the additionalinitiator(s) are added to the batch. Optionally, additional chaintransfer agent(s) can be added. Adjusting the amount of chain transferagent can provide an in-process correction for the product molecularweight obtained from the previous reaction cycle. Other additives,including optional photocrosslinking agents, and optional solvent, canalso be added at this time.

The batch is de-oxygenated, warmed to the runway onset temperature ofthe initiator having the lowest runaway onset temperature, and reactedessentially adiabatically as described above for the previous reactioncycle.

If necessary, additional reaction cycles can be performed to continueincreasing conversion to the desired level.

Optionally, when all of the reaction cycles are complete, unreactedmonomer can be stripped from the batch by pulling vacuum on the hotreaction product in the batch reactor by external vacuum equipment suchas a vacuum pump and optionally condensing monomer vapors in an externalheat exchanger with cooling.

The reaction mixture's viscosity at the temperature at the end of thefinal reaction cycle is typically less than about 200,000 to about500,000 centipoise (Brookfield viscosity at draining temperature) topermit draining of the molten polymer from the reactor and optionallymixing additives into the batch. Typically, inert gas (such as nitrogen)pressure in the head space of the reactor car be used to hasten thedraining of the product from the reactor.

After the reaction mixture is drained, an apparatus such as anextractor-extruder can be used to strip unreacted monomer and/or anysolvent that optionally was added to the batch, or further process thepolymer by mixing in additives comprising plasticizers, tackifiers,antioxidants and/or stabilizers, and extruding the polymer into thephysical form that it is intended to be used (i.e. in sheet form for apressure sensitive adhesive or a release material). One particularlyuseful antioxidant is IRGANOX 1010(tetrakis(methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate))methane)available from Ciba Specialty Chemicals, Tarrytown, N.Y. Thesilicone-containing copolymer can also be dissolved in a solvent topermit the polymer to be solvent coated.

The silicone-containing copolymers may be adhesives, especially pressuresensitive adhesives. The adhesive composition may be coated in a varietyof different ways, either out of solvent or via hot-melt coating to formadhesive articles. In some embodiments the coating process may befollowed by crosslinking, such as, for example by photocrosslinking byexposure to actinic radiation such as UV light.

When the adhesive composition is solvent coated, it may be applied byany conventional application method, including but not limited togravure coating, curtain coating, slot coating, spin coating, screencoating, transfer coating, brush or roller coating, inkjet printing andthe like. The thickness of a coated adhesive layer, typically in theform of a liquid is in part dependent on the nature of the materialsused and the specific properties desired. Exemplary thicknesses of anadhesive layer may be in the range from about 1 to about 250micrometers, 12 to about 200 micrometers or about 25 to 100 micrometers.

When hot melt processing is used, the adhesive composition can be formedinto a film or coating by either continuous or batch processes. Anexample of a batch process is the placement of a portion of the adhesivebetween a substrate to which the film or coating is to be adhered and asurface capable of releasing the adhesive film or coating to form acomposite structure. The composite structure can then be compressed at asufficient temperature and pressure to form an adhesive coating or filmof a desired thickness after cooling. Alternatively, the adhesive can becompressed between two release surfaces and cooled to form an adhesivetransfer tape useful in laminating applications. As with solvent coatedprocesses, the thickness of the adhesive coating may be in the rangefrom about 1 to about 250 micrometers, 12 to about 200 micrometers orabout 25 to 100 micrometers.

Continuous forming methods include drawing the adhesive out of a filmdie and subsequently contacting the drawn adhesive to a moving plasticweb or other suitable substrate. A related continuous method involvesextruding the adhesive and a coextruded backing material from a film dieand cooling the layered product to form an adhesive tape. Othercontinuous forming methods involve directly contacting the adhesive to arapidly moving plastic web or other suitable preformed substrate. Usingthis method, the adhesive is applied to the moving preformed web using adie having flexible die lips, such as a rotary rod die. After forming byany of these continuous methods, the adhesive films or layers can besolidified by quenching using both direct methods (e.g., chill rolls orwater baths) and indirect methods (e.g., air or gas impingement).

The adhesive composition may be disposed on a substrate either bysolvent coating or hot melt coating. The substrate may be a releaseliner, a rigid surface, a tape backing, a film, or a sheet. The adhesivecomposition can be coated onto a release liner, coated directly onto asubstrate, a film or a backing, or formed as a separate layer (e.g.,coated onto a release liner) and then laminated to a substrate or film.In some embodiments the adhesive is a transfer tape, i.e. it is disposedbetween two release liners.

In some embodiments it may be desirable to impart a microstructuredsurface to one or both major surfaces of the adhesive. It may bedesirable to have a microstructured surface on at least one surface ofthe adhesive to aid air egress during lamination. If it is desired tohave a microstructured surface on one or both surfaces of the adhesivefilm, the adhesive coating or film may be placed on a tool or a linercontaining microstructuring. The liner or tool can then be removed toexpose an adhesive film having a microstructured surface. Generally withoptical applications it is desirable that the microstructure disappearover time to prevent interference with optical properties.

The substrate included in the adhesive article can contain polymericmaterials, glass materials, ceramic materials, metal-containingmaterials (e.g., metals or metal oxides), or a combination thereof. Thesubstrate can include multiple layers of material such as a supportlayer, a primer layer, a hard coat layer, a decorative design, and thelike. The substrate can be permanently or temporarily attached to anadhesive film. For example, a release liner can be temporarily attachedand then removed for attachment of the adhesive film to anothersubstrate.

The substrate can have a variety of functions such as, for example,providing flexibility, rigidity, strength, support, or opticalproperties such as, for example, reflectivity, antireflectivity,polarization, or transmissivity (e.g., selective with respect todifferent wavelengths). That is, the substrate can be flexible or rigid;reflective or non-reflective; visibly clear, colored but transmissive,or opaque (e.g., not transmissive); and polarizing or non-polarizing.

Representative examples of polymeric substrates include those thatcontain polycarbonates, polyesters (e.g., polyethylene terephthalatesand polyethylene naphthalates), polyurethanes, poly(meth)acrylates(e.g., polymethyl methacrylates), polyvinyl alcohols, polyolefins suchas polyethylenes and polypropylenes, polyvinyl chlorides, polyimides,cellulose triacetates, acrylonitrile-butadiene-styrene copolymers, andthe like.

In other embodiments, the substrate is a release liner. Any suitablerelease liner can be used. Examples of suitable liners include paper,e.g., kraft paper, or polymeric films, e.g., polyethylene, polypropyleneor polyester. At least one surface of the liner can be treated with arelease agent such as silicone, a fluorochemical, or other low surfaceenergy based release material to provide a release liner. Suitablerelease liners and methods for treating liners are described in, e.g.,U.S. Pat. Nos. 4,472,480, 4,980,443 and 4,736,048. The liner can have amicrostructure on its surface that is imparted to the adhesive to form amicrostructure on the surface of the adhesive film. The liner can thenbe removed to expose an adhesive film having a microstructured surface.

The silicone-containing copolymer may be used alone as an adhesive or itmay contain a variety of additives. For example, additional adhesivepolymers or elastomeric polymers may be blended with thesilicone-containing copolymer to form the adhesive composition.Additionally, other optional property modifying additives can be mixedwith the adhesive composition. Typical property modifiers includetackifying agents (tackifiers) and plasticizing agents (plasticizers) tomodify the adhesive performance of the formed adhesive composition. Inaddition, other property modifiers, such as fillers, may be added ifdesired, provided that if and when incorporated, such additives are notdetrimental to the properties desired in the final composition. Fillers,such as fumed silica, fibers (e.g., glass, metal, inorganic, or organicfibers), carbon black, glass or ceramic beads/bubbles, particles (e.g.,metal, inorganic, or organic particles), polyaramids (e.g., thoseavailable from DuPont Chemical Company; Wilmington, Del. under the tradedesignation, KEVLAR), and the like which can be added in amounts up toabout 30% by weight. Other additives such as dyes, inert fluids (e.g.,hydrocarbon oils), pigments, flame retardants, stabilizers,antioxidants, compatibilizers, antimicrobial agents (e.g., zinc oxide),electrical conductors, thermal conductors (e.g., aluminum oxide, boronnitride, aluminum nitride, and nickel particles), and the like can beblended into these systems in amounts of generally from about 1 to about50 percent by total volume of the composition.

The silicone-containing copolymers may be release materials. Releasematerials are materials that exhibit low adhesion to an adhesive, suchas a pressure sensitive adhesive, so that separation can occursubstantially between the adhesive and release material interface.Release coatings can be used as a “liner” for adhesive articles, such aslabels or medical dressing bandages, and the like where the adhesivearticle is generally supplied as a sheet-like construction, as opposedto a roll-like construction. In tape applications, a release material isoften referred to as a “low adhesion backsize,” or LAB. In this form,the adhesive surface contacts the back surface of the article. The LABprevents the adhesive from permanently adhering to the back surface ofthe article and allows that article to be unwound.

A wide variety of release articles may be prepared using thesilicone-containing polymers of this disclosure. Among the articles arerelease liners, tape constructions, and sheet constructions. Generally,the release performance requirements are different for release linersthan for LAB materials. Typically it is desirable to have higheradhesion levels between the adhesive and the release components in tapeconstructions (LABs) because it is desirable for the tape to notspontaneously unroll. Spontaneous unrolling and similar phenomena mayoccur if the adhesion level between the release and adhesive componentare too low.

The composition of the copolymer is such as to provide the copolymerwith a surface release value not greater than about 50 N/dm. It shouldbe understood that this upper limit of 50 N/dm applies to use withhighly aggressive pressure sensitive adhesives which have peel adhesionvalues of 100 N/dm or higher. Pressure sensitive adhesives as a groupmay be categorized into three broad categories (1) low (5-15 N/dm), (2)intermediate (25-50 N/dm), and (3) high (60-100 plus N/dm) peel adhesionranges. The degree of release can be selected to match theaggressiveness of the pressure sensitive adhesive with which it will bein contact and it is only for the most aggressive pressure sensitiveadhesives that a release value as high as 50 N/dm would be selected.Release coatings for less aggressive pressure sensitive adhesives wouldbe selected to be correspondingly lower.

Coatings of the silicone-containing copolymer of this disclosure mayhave release levels for a given pressure sensitive adhesive that can besystematically changed from a tight low adhesion backsize level (15 to30 N/dm) to a premium release liner level (0.2 to 0.6 N/dm) by variationin the amount and type of silicone present. This, coupled with utilityfor a variety of pressure sensitive adhesive types, allows for theserelease materials to satisfy a wide range of application needs. Sincesilicone constitutes only a portion of the coating (even at easy levelsof release suitable for release liner applications), these copolymercompositions provide a potential cost savings over conventional 100%silicone release compositions and numerous blends.

The release composition may be coated in a variety of different ways,either out of solvent or via hot-melt coating, including byco-extrusion, to form articles. In some embodiments the coating processmay be followed by crosslinking, such as, for example byphotocrosslinking by exposure to actinic radiation such as UV light.

When the release composition is solvent coated, it may be applied by anyconventional application method, including but not limited to gravurecoating, curtain coating, slot coating, spin coating, screen coating,transfer coating, brush or roller coating, inkjet printing and the like.The thickness of a coated release layer, typically in the form of aliquid is in part dependent on the nature of the materials used and thespecific properties desired. Exemplary thicknesses of a release layermay be in the range from about 0.01 to about 2.5 micrometers, or about0.5 to 1.0 micrometers.

When hot melt processing is used, typically continuous processes areused. Continuous forming methods include drawing the release materialout of a film die and subsequently contacting the drawn release materialto a moving plastic web or other suitable substrate. A relatedcontinuous method involves extruding the release material and acoextruded backing material from a film die and cooling the layeredproduct to form a release article. Other continuous forming methodsinvolve directly contacting the release material to a rapidly movingplastic web or other suitable preformed substrate. Using this method,the release material is applied to the moving preformed web using a diehaving flexible die lips, such as a rotary rod die. After forming by anyof these continuous methods, the release films or layers can besolidified by quenching using both direct methods (e.g., chill rolls orwater baths) and indirect methods (e.g., air or gas impingement).

The release coatings may comprise the silicone-containing copolymeralone, or may comprise such copolymers blended with a compatiblehomopolymer, copolymer, etc. The low percentage of silicone blockcontained in the copolymers makes the copolymers readily compatible withpolymers of similar composition to the vinyl polymeric blocks orsegments. Examples of suitable polymers and copolymers include, forexample, thermoplastic polymers such as olefins, polyesters, orrenewable polymers such as polylactic acid, and the like. Particularlysuitable polymers include olefins such as polyethylene, polypropylene,copolymers of ethylene and propylene, and the like. Fillers or pigments(e.g., alumina, silica, titania, or calcium carbonate) may, of course,be added to the copolymer compositions to reduce gloss and also impart asurface texture that is more receptive to marking with pencils androller ball pens.

A blend of the silicone-containing copolymer and a thermoplastic polymermay be coated onto a substrate via coating (such as hot melt coating) orcoextrusion, or the blend may be extruded as a stand alone film.

The silicone-containing release copolymers may be used as a coating fora solid substrate, which may be a sheet, fiber, or shaped object. Amongthe preferred substrates are flexible substates used for pressuresensitive adhesive products. Suitable substrates include paper, metalsheets and foils, non-woven fabrics, and films of thermoplastic resinssuch as polyesters, polyamides, polyolefins, polycarbonates, polyvinylchloride, etc., although any surface requiring release toward adhesivescan be used. Primers known in the art can be utilized to aid in adhesionof the coating to the substrate, but they are not generally necessary.

The release coating compositions may be applied to suitable substratesby means of conventional coating techniques such as wire-wound rod,direct gravure, offset gravure, reverse roll, air-knife, and trailingblade coating; hot melt coating is also possible. The resultant coatingsprovide effective release for a wide variety of conventional pressuresensitive adhesives such as natural rubber-based, acrylic, and othersynthetic film-forming elastomeric materials.

The present disclosure provides a roll of tape which includes a flexiblebacking member, a pressure sensitive adhesive coating one major surfaceof the backing member, and a release coating on the opposite majorsurface of the backing comprising the polymer defined above. Thedisclosure further provides a tape comprising a flexible backing member,a pressure sensitive adhesive coating one major surface of the backingmember and a release liner comprising a flexible sheet coated over themajor surface adhered to the pressure sensitive coating with thecopolymer defined above. The disclosure further provides a transfer tapecomprising a film of pressure sensitive adhesive between two releaseliners, at least one being coated with the copolymer.

The disclosure also provides a coated sheet material wherein the releaseagent is on one side of the sheet and the adhesive is on the other side.The disclosure further provides a coated sheet material wherein theadhesive is a normally tacky and pressure sensitive adhesive. Thedisclosure also provides a stack of superimposed sheets of the coatedsheet material, the pressure sensitive adhesive on each sheet being incontact with the release agent on an immediately adjacent sheet.

The disclosure also provides a fanfolded web formed from the coatedsheet material, the adhesive on each segment of the web being in contactwith the release agent on an immediately adjacent segment. Thedisclosure also provides the coated sheet material wherein the adhesiveis present in a band adjacent one edge of the sheet. The disclosure alsoprovides a stack of individual sheets formed from the coated sheetmaterial, the adhesive bands of adjacent sheets lying along oppositeedges. The disclosure further provides a coated sheet material having arelease agent on one side and an adhesive on the other side wherein saidcoated sheet material can be wound convolutedly on itself about a coreto form a roll. The disclosure further provides the coated sheetmaterial wherein the adhesive is a normally tacky pressure sensitiveadhesive.

The disclosure further provides a coated sheet material wherein therelease agent covers a first portion of one side and a normal tacky andpressure sensitive adhesive covers a second portion of the same side.The disclosure further provides a coated sheet material wherein thesheet is an elongate strip having spaced alternating areas of releaseagent and an adhesive. The disclosure also further provides the coatedsheet material wherein the sheet is generally rectangular, the releaseagent being present in a band adjacent one edge and the pressuresensitive adhesive being present in a band adjacent the opposite edge.

The silicone-containing copolymers comprising the release coating have awell-defined structure. When such copolymers are coated on a substrate,the silicone segment is thought to present a low energy, “siliconized”release surface, and the higher energy copolymerized polymeric blocks orsegments are thought to provide adhesion to the base material.Similarly, if the silicone-containing copolymers are coextruded withother polymeric materials to form a release article, the higher energycopolymerized blocks or segments are thought to provide improvedcompatibility with these materials. The chemical nature or compositionof the higher energy copolymerized blocks or segments can be modifiedindependently of the free radically polymerizable silicone-containingmonomer(s) to alter properties other than the release properties. Suchproperties include, for example, adhesion to the substrate, waterdispersability, ink receptivity, etc. which can be altered without anyserious perturbation of the surface characteristics of the film. Therelease properties of the coating are determined by both the siliconecontent (weight percentage) of the copolymer and the molecular weight ofthe silicone segment, with higher silicone content and/or molecularweight providing easier release. A copolymer or copolymer blend can,therefore, be chemically tailored to provide a specific level of releasewhich can be reproduced with consistency, thus making possible thevariation of the release properties of a backing over a range of valuesin a controlled fashion.

The silicone-containing release copolymers of this disclosure can beused to prepare structured adhesive articles. Several approaches tostructuring adhesives are known, including those shown in, for example,U.S. Pat. Nos. 5,296,277 and 5,362,516 (both Wilson et al.); U.S. Pat.Nos. 5,141,790 and 5,897,930 (both Calhoun et al.); and U.S. Pat. No.6,197,397 (Sher et. al). These patents disclose how the structure in theadhesive is built from the interface between the adhesive and therelease liner.

These release liners are generally manufactured by structuring athermoplastic polymer surface of the liner. Current methods of makingrelease liners having microstructured patterns include cast extrusiononto a microstructured tool that imparts the desired pattern to theliner followed by silicone release coating where required, or bypressing a pattern into a thermoplastic polymer surface, with or withouta silicone release coating, between structured nips to impart a pattern.These manufacturing steps form the topography on the liner, which isthen used to impart topography into an adhesive.

EXAMPLES

These examples are merely for illustrative purposes only and are notmeant to be limiting on the scope of the appended claims. All parts,percentages, ratios, etc. in the examples and the rest of thespecification are by weight, unless noted otherwise. Solvents and otherreagents used were obtained from Sigma-Aldrich Chemical Company;Milwaukee, Wis. unless otherwise noted.

Table of Abbreviations Abbreviation or Trade Designation DescriptionInitiator-1 Thermal free radical initiator of 2,2′-azobis(2,4dimethylpentanenitrile) commercially available from E. I. duPont deNemours & Co, Wilmington, DE as “VAZO 52”. Initiator-2 Thermal freeradical initiator of 2,2′-azobis(cyclo- hexanecarbonitrile) commerciallyavailable from E. I. duPont de Nemours & Co, Wilmington, DE as “VAZO88”. Antioxidant- Antioxidant tetrakis(methylene(3,5-di-tert-butyl- 14-hydroxyhydrocinnamate))methane commercially available from CibaSpecialty Chemicals, Tarrytown, NY as “IRGANOX 1010”. Initiator-3Thermal free radical initiator of 2,2′-azobis(2- methylbutyronitrile)commercially available from E. I. duPont de Nemours & Co, Wilmington, DEas “VAZO 67”. Initiator-4 Thermal free radical initiator of2,5-dimethyl- 2,5-Di-(t-butylperoxy)hexyne-3 commercially available fromElf Atochem, Philadelphia, PA as “LUPERSOL 130”. Initiator-5 Thermalfree radical initiator of azo-bis(iso- butyronitrile) commerciallyavailable from E. I. duPont de Nemours & Co, Wilmington, DE as “VAZO64”. Initiator-6 Thermal free radical initiator of 2,5-dimethyl-2,5-di-(tert-butylperoxoxy)hexane commercially available from ArkemaCanada, Inc., Oakville, ON as “LUPEROX 101”. IOA Isooctyl acrylate ABPCopolymerizable photoinitiator of 4-acryloxy benzophenone, preparedaccording to U.S. Pat. No. 4,737,559 (Kellen et al.). IOTGIsooctylthioglycoate commercially available from Dow Chemical, Midland,MI. SiMac Silicone macromer, methacrylate terminated poly-dimethylsiloxane, prepared as described in Synthesis Example S1 below.EA Ethyl acetate PET Film An aminated-polybutadiene primed polyesterfilm of polyethylene terephthalate having a thickness of 38 micrometers.ODA Octadecyl acrylate MA Methyl acrylate AA Acrylic Acid MMA Methylmethacrylate MAA Methacrylic acid AN Acrylonitrile MFSMercapto-functional polydimethylsiloxane, commer- cially available fromShinEtsu Silicones, Akron, OH as “KF-2001”. LDPE Low densitypolyethylene, commercially available as EXXON 129.24 from ExxonMobil,Houston, TX. Additive- A color concentrate of 4% of silver black #3 in 1LDPE resin available from PolyOne, Elk Grove Village, IL as“CC10100332WE”. Additive- A light stabilizer concentrate in LDPEavailable 2 from Ampacet Corp., Tarrytown, NY as “10407”. Packaging Tapeof 4.8 centimeter (1.88 inch) width commer- Tape cially available from3MCompany, St. Paul, MN as “3M SCOTCH Box Sealing Tape3750”. The tape wascut to 2.54 centimeter (1 inch) width for use in the testing. THFtetrahydrofuranTest MethodsInherent Viscosity (IV)

Average inherent viscosities (IV) were measured at 30° C. using aCanon-Fenske viscometer (Model No. 50 P296) in a THF solution at 30° C.at a concentration of 0.2 g/dL. Inherent viscosities of the materialstested were found to be essentially independent of concentration in therange of 0.1 to 0.4 g/dL. The average inherent viscosities were averagedover 3 or more runs. Any variations for determining average inherentviscosities are set forth in specific Examples.

180° Peel Adhesion

This peel adhesion test is similar to the test method described in ASTMD 3330-90, substituting a glass substrate for the stainless steelsubstrate described in the test. Adhesive coatings on polyester filmwere cut into 1.27 centimeter by 15 centimeter strips. Each strip wasthen adhered to a 10 centimeter by 20 centimeter clean, solvent washedglass coupon using a 2-kilogram roller passed once over the strip. Thebonded assembly dwelled at room temperature for about one minute and wastested for 180° peel adhesion using an IMASS slip/peel tester (Model3M90, commercially available from Instrumentors Inc., Strongsville,Ohio) at a rate of 2.3 meters/minute (90 inches/minute) over a fivesecond data collection time. Two samples were tested; the reported peeladhesion value is an average of the peel adhesion value from each of thetwo samples. The data was recorded in ounces per inch and converted toNewtons per decimeter (N/dm).

Release Test

Samples were prepared for release testing by attaching laminates ofadhesive tape on the experimental release film to a 15.2 centimeter by30.5 centimeter glass panel using double-coated adhesive tape(commercially available from 3M Company under the trade designation“410B”) via the non-release side of the release film using a 2 kg rubberroller. The laminated adhesive tape was then peeled from theexperimental release liner at 180° at a rate of 2.3 meters/minute (90inches/minute). All tests were done in a facility at constanttemperature (20° C.) and constant humidity (50% RH). In the case ofshocky peel, the minimum, maximum and average peel values are allreported to indicate the level of shockiness and a description of thepeel was also included. To determine the readhesion value, the peeledadhesive tape was applied to the surface of a clean glass plate by meansof a 2 kg rubber roller. The readhesion value was a measure of the forcerequired to pull the tape from the glass surface at an angle of 180° ata rate of 2.3 meters/minute (90 inches/minute). The peel tester used forall examples was an IMass slip/peel tester (Model 3M90, commerciallyavailable from Instrumentors Inc., Strongville, Ohio). Measurements wereobtained in ounces/inch and converted to Newtons per decimeter.

Synthesis Examples Synthesis Example S1: Preparation of SiMac

A methacrylate-terminated polydimethylsiloxane macromer was prepared asdescribed in U.S. Pat. No. 4,693,935 (Mazurek) “Monomer C 3b”. Themacromer, having an average molecular weight of about 10,000 grams/mole,was prepared using BuLi initiator. A flame-dried 1 liter three-neckedflask equipped with a mechanical stirrer, condenser, and septum andpurged with dry argon was charged with a dilute solution of D3 (1 gram)in heptane (100 milliliters), both freshly dried. 5.5 milliliters ofBuLi (1.7 M in hexane) (9.35 mmoles) was introduced and the initiationreaction was continued overnight at room temperature. 198.7 grams (0.89mole) of D3 in THF (496.8 g) was introduced into the reaction flask viapolytetrafluoroethylene (PTFE) tubing and the polymerization wascontinued for 8 hours with the reaction mixture maintained at roomtemperature. Progress of the reaction was monitored by GC analysis ofthe reaction mixture. Thereafter the capping agent,3-methacryloxypropyldimethylchlorosilane (2.26 g, 10.3 mmoles), wasintroduced and the reaction mixture was stirred for 1 hour, whileadditionally agitated with an ultrasonic bath which raised thetemperature to about 40° C. The resultant polymer solution was pouredinto an excess of methanol with vigorous stirring. The separated polymerfraction was dissolved in ethyl ether and washed with water. The organiclayer was dried with magnesium sulfate, filtered, and evaporated. Theresultant polymer did not contain detectable quantities of low molecularweight materials, such as oligomeric siloxanes. The macromer producedwas analyzed by gel permeation chromatography which gave the followingresults: M_(n)=12,881, M_(w)=14,756, and polydispersity of 1.14.

Comparative Example C-1

A sample was prepared as described in U.S. Pat. No. 4,693,935 (Mazurek)Example 64. In a glass reaction bottle was placed 83 parts by weightIOA, 7 parts by weight AA, 10 parts by weight SiMac, 0.3 parts by weightInitiator-5 and 150 parts by weight EA. The reaction bottle was purgedwith nitrogen and sealed. It was placed in a 55° C. bath and tumbledtherein for 24 hours. The resulting polymer solution was diluted with250 parts by weight EA and knife coated onto a PET film and dried toprovide a dry coating thickness of 25 micrometers.

Examples 1-4

For Examples 1-4 essentially adiabatic polymerizations were carried outby a two step reaction within a VSP2 adiabatic reaction apparatusequipped with a 316 stainless steel test can (available from Fauske andAssociates Inc, Burr Ridge Ill.). In the VSP2 reaction vessel was placedIOA, AA, SiMac, Initiator-1, IOTG and ABP in the amounts shown inTable 1. The reactor was sealed and purged of oxygen. The reactionmixture was heated to 60° C. and the reaction proceeded adiabatically.Typical reaction peak temperature was 150° C. When the reaction wascomplete, the mixture was cooled to below 50° C. To the reaction productof the first step was added 0.7 grams of a mixture, (the contents of theadditive mixture are shown in Table 2) and 0.2188 grams of ABP. Thereactor was sealed and purged of oxygen. The reaction mixture was heatedto 60° C. and the reaction proceeded adiabatically. Typical reactionpeak temperature was 160° C. The samples were removed from the reactor,Inherent Viscosity (IV) was measured using the Test Method given aboveand is shown in Table 3. The polymer samples were dissolved in THF atapproximately 30% solids. The polymer solutions were knife coated onto aPET film and dried to provide a dry coating thickness of 25 micrometers.The coated samples were post-crosslinked by passing under a highintensity UV source (“D” or “H” bulb) such that each pass gave a UV doseof 600 milliJoules per square centimeter. Samples were tested for 180°Peel Adhesion using the Test Method given above, both immediately afteradhering and after dwelling for 24 hours. These data are shown in Table3.

TABLE 1 IOA AA SiMac Initiator-1 IOTG ABP Example (parts) (parts)(parts) (parts) (parts) (parts) 1 85 10 5 0.004 0.045 0.3125 2 80 10 100.004 0.06 0.3125 3 80 10 10 0.004 0.08 0.3125 4 80 10 10 0.004 0.150.3125

TABLE 2 Example Additive IOTG Initiator-1 Initiator-2 Initiator-4 EAMixture (parts) (parts) (parts) (parts) (parts) 1 4.2 0.5 0.1 0.15 45.052 5.58 0.5 0.1 0.15 43.67 3 7.44 0.5 0.1 0.15 41.81 4 13.95 0.5 0.1 0.1535.3

TABLE 3 180° Peel UV Cure Initial 180° Adhesion after IV (Number of PeelAdhesion 24 Hour Dwell Example (dl/g) passes) (N/dm) (N/dm) 1 0.55 1 8.6110.7 2 0.62 1 1.9 100.3 3 0.37 3 40.3 111.0 4 0.29 4 8.6 100.4 C1 0.61NA 42.6 88.5 NA = Not Applicable

Examples 5-7

For Examples 5-7 essentially adiabatic polymerization was carried out bya two step reaction within a VSP2 adiabatic reaction apparatus equippedwith a 316 stainless steel test can (available from Fauske andAssociates Inc, Burr Ridge Ill.). In the VSP2 reaction vessel was placedODA, AN, MA, AA, IOTG and SiMac or MFS in the amounts shown in Table 4.To the mixture was added 0.1 grams of Antioxidant-1 and 1.03 grams of amixture (the contents of the additive mixture are shown in Table 5). Thereactor was sealed and purged of oxygen. The reaction mixture was heatedto 63° C. and the reaction proceeded adiabatically. Typical reactionpeak temperature was 165° C. When the reaction was complete, the mixturewas cooled to below 75° C. To about 70 grams of the reaction product ofthe first step was added 0.7 grams of a mixture (the contents of theadditive mixture are shown in Table 6) and in Example 5, added 0.35grams IOTG. The reactor was sealed and purged of oxygen. The reactionmixture was heated to 65° C. and the reaction proceeded adiabatically.Typical reaction peak temperature was 160° C. The samples were removedfrom the reactor, Inherent Viscosity (IV) was measured using the TestMethod given above, with the exception that Examples 6 and 7 were in a70:30 THF/toluene solution at a concentration of about 0.7 g/dL andExample 5 was in EA at a concentration of 0.3 g/dL, and provided theresults shown in Table 7.

Samples of the polymer from Examples 5 and 7 were dissolved in EA to 5%solids solutions, coated onto PET using a Number 6 Mayer rod and driedin a 65° C. oven for 30 minutes to yield a release surface. The releasesurface was tested by adhering samples of SCOTCH MAGIC tape 810(commercially available from 3M Company, St. Paul, Minn.) to the releasesurface, aging for the specified time period and conditions, andconducting the Release Test described in the Test Method above. TheResults are shown in Tables 8 and 9.

Examples 8 and 9

For Examples 8-9 essentially adiabatic polymerizations were carried outby a one step reaction within a VSP2 adiabatic reaction apparatusequipped with a 316 stainless steel test can (available from Fauske andAssociates Inc, Burr Ridge Ill.). In the VSP2 reaction vessel was placedODA, AN, MA, AA and MFS in the amounts shown in Table 4. To the mixturewere added 0.1 grams of Antioxidant-1 and 1.03 grams of a mixture (thecontents of the additive mixture are shown in Table 5). The reactor wassealed and purged of oxygen. The reaction mixture was heated to 63° C.and the reaction proceeded adiabatically. Typical reaction peaktemperature was 165° C. The samples were removed from the reactor,Inherent Viscosity (IV) was measured using the Test Method given above,with the exception that Examples 8 and 9 were in a 70:30 THF/toluenesolution at a concentration of about 0.5 g/dL and provided the resultsshown in Table 7.

TABLE 4 ODA AN MA AA SiMac MFS IOTG Example (parts) (parts) (parts)(parts) (parts) (parts) (parts) 5 30 25 10 5 30 0 3 6 30 25 10 5 30 0 17 30 25 10 5 0 30 0 8 30 22 5 3 0 40 0 9 27 15 5 3 0 50 0

TABLE 5 Example Additive Initiator-1 Initiator-2 Initiator-6 Initiator-4MA Mixture (parts) (parts) (parts) (parts) (parts) 5 0.1 0.1 0.05 0 10 60.1 0.1 0 0 10 7 0.1 0.1 0.05 0 10 8 0.1 0.1 0.05 0.05 10 9 0.1 0.1 0.050.05 10

TABLE 6 Example Additive IOTG Initiator-1 Initiator-2 Initiator-4Initiator-6 EA Mixture (parts) (parts) (parts) (parts) (parts) (parts) 50 0.5 0.5 0.1 0.5 48.4 6 3.5 0.5 0.5 0.1 0.5 44.9 7 0 0.5 0.5 0.1 0.548.4

TABLE 7 IV Wt % Solids (based on Example (dl/g) total wt of mixture) 50.11 93.5 6 0.14 95.2 7 0.09 85.2 8 0.13 90.0 9 0.19 98.3

Comparative Example C2

A double layer of SCOTCH MAGIC tape 810 (commercially available from 3MCompany, St. Paul, Minn.) was peeled from a roll and aged for thespecified time period and conditions. The top layer of the double layerwas tested for peel and readhesion as described in the Test Methodabove. The Results are in Tables 8 and 9.

TABLE 8 180° Peel Readhesion 180° Peel Readhesion after 3 days after 3days after 3 days after 3 days at RT at RT at 65° C. at 65° C. Example(N/dm) (N/dm) (N/dm) (N/dm) 7 2.26 25.6 4.88 18.6 C2 7.47 10.1 19.919.19

TABLE 9 180° Peel Readhesion 180° Peel Readhesion after 2 days after 2days after 2 days after 2 days at RT at RT at 65° C. at 65° C. Example(N/dm) (N/dm) (N/dm) (N/dm) 5 1.89 10.8 1.98 0.77 C2 5.76 8.8 23.64 10.8

Example 10

Extruded release film was prepared using a dry blended mixture of 95parts by weight LDPE and 5 parts by weight the polymer produced inExample 7. The mixture was fed into a 1.9 centimeter (0.75 inch)Brabender extruder with a mixing screw. After melting and mixing, theextrudate was forced through a 15.2 centimeter (6 inch) flat castextrusion die to form a molten film. Extrusion temperatures of 110, 115,120, 140, and 140° C. were used, extrusion pressure was 2,960 to 3,450kiloPascals (430 to 500 pounds) at a rate of 90 RPM. The molten film waspassed through a chilled roll stack to cool and solidify the resins intofinal finished film form. The resultant film was transparent. Togenerate samples for release testing, the adhesive side of 3M SCOTCHCALELECTROCUT Graphic Film 7725-10 (commercially available from 3M Company,St. Paul, Minn.) was laminated to the molten polymer before entering thechilled nip. Upon cooling and aging approximately one week, 2.54centimeter (1 inch) wide strips were cut from the roll and tested forrelease value using the Test Method described above (readhesion testingwas not carried out), giving a release value of 2.62 N/dm.

Comparative Example C3

Extruded release film was prepared as described in Example 7 using onlyLDPE. Extrusion temperatures of 185, 190, 195, 200, and 200° C. wereused. To generate samples for release testing, the adhesive side of 3MSCOTCHCAL ELECTROCUT Graphic Film 7725-10 (commercially available from3M Company, St. Paul, Minn.) was laminated to the molten polymer beforeentering the chilled nip. Upon cooling and aging approximately one week,2.54 centimeter (1 inch) wide strips were cut from the roll and testedfor release value using the Test Method described above (readhesiontesting was not carried out), giving a release value of 4.47 N/dm.

Example 11

For Example 11, essentially adiabatic polymerization was carried out bya two step reaction within a VSP2 adiabatic reaction apparatus equippedwith a 316 stainless steel test can (available from Fauske andAssociates Inc, Burr Ridge Ill.). In the VSP2 reaction vessel was placedMA (49 grams), MMA (20 grams), MAA (5 grams), IOTG (0.3 grams) and MFS(25 grams). To the mixture was added 0.1 grams of Antioxidant-1 and 1.02grams of a mixture containing: Initiator-1 (0.1 gram) and Initiator-3(0.1 gram) dissolved in 10 grams of MA. The reactor was sealed andpurged of oxygen. The reaction mixture was heated to 59° C. and thereaction proceeded adiabatically. Typical reaction peak temperature was170° C. When the reaction was complete, the mixture was cooled to below65° C. To about 70 grams of the reaction product of the first step wasadded 0.7 grams of a mixture containing: Initiator-1 (0.2 gram),Initiator-2 (0.2 gram), Initiator-4 (0.04 gram) and Initiator-6 (0.2gram) dissolved in 19.36 grams of EA. The reactor was sealed and purgedof oxygen. The reaction mixture was heated to 59° C. and the reactionproceeded adiabatically. Typical reaction peak temperature was 190° C.The samples were removed from the reactor, Inherent Viscosity (IV) wasmeasured using the Test Method given above and was found to be 0.25dl/gm.

Example 12

The polymer produced in Example 11 was cooled with liquid nitrogen andfed through an IKA Werke MF-10 grinder at 3000 rpm with a 2.0 mm sieveat the outlet of the grinder to provide a granular material. Thismaterial (10 parts by weight) was dry blended with LDPE (90 parts byweight) and fed into a 1.0 inch twin screw conical extruder with amixing screw. The extrudate was passed through a strand die into a 0° C.water bath and the resulting strand was cut into 0.125 inch roundpellets. The pellets were dried in a 65.5° C. oven for 24 hours.

The blended pellets from above (50 parts) were further dry blended withLDPE (45 parts), Additive-1 (1 part) and Additive-2 (4 parts). Themixture was fed into a 1.9 centimeter (0.75 inch) Brabender extruderwith a mixing screw (top layer). Another 1.9 centimeter (0.75 inch)Brabender extruder with a mixing screw (bottom layer) was fed with a dryblended mixture of LDPE (96 parts) and Additive-2 (4 parts). Theextrudate from the two extruders was forced through a 15.2 centimeter (6inch) flat cast 2-layer extrusion die to form a molten film withapproximately 1:2 ratio of top layer: bottom layer. Extrusiontemperatures of 160, 170, and 190° C. were used. The molten film waspassed through a chilled roll stack to cool and solidify the resins intofinal finished film form. The resultant film was semi-transparent with asilver tone. Samples of the film were laminated with Packaging Tape. Thesamples were placed in a 65° C. oven for 10 days, then cooled to 20° C.prior to testing. The samples were tested for peel and readhesion asdescribed in the Release Test Method above. The data are presented inTable 10.

Example 13

The blended pellets from Example 12 (70 parts) were further dry blendedwith LDPE (25 parts), Additive-1 (1 part) and Additive-2 (4 parts). Themixture was fed into a 1.9 centimeter (0.75 inch) Brabender extruderwith a mixing screw (top layer). Another 1.9 centimeter (0.75 inch)Brabender extruder with a mixing screw (bottom layer) was fed with LDPE.The extrudate from the two extruders was forced through a 15.2centimeter (6 inch) flat cast 2-layer extrusion die to form a moltenfilm with approximately 1:2 ratio of top layer: bottom layer. The moltenfilm was passed through a chilled roll stack to cool and solidify theresins into final finished film form. The resultant film wassemi-transparent with a silver tone. Samples of the film were laminatedwith Packaging Tape. The samples were placed in a 65° C. oven for 10days, then cooled to 20° C. prior to testing. The samples were testedfor peel and readhesion as described in the Release Test Method above.The data are presented in Table 10.

Comparative Example C4

The reverse side of the film from Example 12 was laminated withPackaging Tape. The samples were placed in a 65° C. oven for 10 days,then cooled to 20° C. prior to testing. The samples were tested for peeland readhesion as described in the Release Test Method above. The dataare presented in Table 10.

TABLE 10 180° Peel after Readhesion after 10 days at 65° C. 10 days at65° C. Example (N/dm) (N/dm) 12 32.2 22.5 13 34.0 16.4 C4 44.9 15.8

What is claimed is:
 1. A method comprising: providing a first reactionmixture comprising: a mercapto-functional silicone; at least oneethylenically unsaturated monomer; a chain transfer agent separate fromthe mercapto-funcitonal silicone; and a thermal initiator; deoxygenatingthe first reaction mixture; heating the first reaction mixture to atemperature above the activation temperature of the thermal initiator;allowing the first reaction mixture to polymerize under essentiallyadiabatic conditions to yield an at least partially polymerized mixture;cooling the at least partially polymerized mixture; adding an additionalthermal initiator to the partially polymerized mixture to form a secondreaction mixture; deoxygenating the second reaction mixture; heating thesecond reaction mixture to a temperature above the activationtemperature of the additional thermal initiator; allowing the secondreaction mixture to polymerize under essentially adiabatic conditions toform a polymer.
 2. The method of claim 1, wherein themercapto-functional silicone has the structure:(R¹)_(3-x)(HSR²)_(x)Si—(OSiR⁵R⁶)_(y)—OSi(R³)_(3-q)(R⁴SH)_(q) whereineach R¹ is independently an alkyl, aryl, alkaryl, alkoxy, alkylamino,hydroxyl, hydrogen, or fluoroalkyl group; each R² is a divalent linkinggroup; each R³ is an alkyl, aryl, alkaryl, alkoxy, alkylamino, hydroxyl,hydrogen, or fluoroalkyl group; each R⁴ is a divalent linking group;each R⁵ is an alkyl, aryl, alkaryl, alkoxy, alkylamino, hydroxyl,fluoroalkyl, hydrogen, or —ZSH, wherein Z is a divalent linking group;each R⁶ is an alkyl, aryl, alkaryl, alkoxy, alkylamino, hydroxyl,fluoroalkyl, hydrogen, or —ZSH, wherein Z is a divalent linking group; xis an integer of 0-3; y is an integer of 10 or greater; and q is aninteger of 0-3.
 3. The method of claim 1, wherein themercapto-functional silicone has a number average molecular weight offrom 2,000-20,000 grams/mole and from 1-20 mole % —CH₂CH₂CH₂SH groups.4. The method of claim 1, wherein the mercapto-functional silicone has anumber average molecular weight of from 5,000-10,000 grams/mole and from2-4 mole % —CH₂CH₂CH₂SH groups.
 5. The method of claim 1, wherein theethylenically unsaturated monomer comprises an alkyl (meth)acrylatewhich as a homopolymer has a Tg above about 30° C.
 6. The method ofclaim 5, wherein the alkyl (meth)acrylate monomer comprises an alkyl(meth)acrylate with an alkyl chain having from 1-20 carbon atoms.
 7. Themethod of claim 1, further comprising the steps of: isolating thepolymer; and coating the polymer on a substrate.
 8. The method of claim7, wherein the coating step comprises hot melt coating, solvent coatingor coextrusion.
 9. The method of claim 7, wherein the polymer comprisesa release material and the substrate comprises a film or a tape backing.10. The method of claim 8, wherein the coating method comprises hot meltcoating and the coating thickness is in the range from about 0.01 toabout 2.5 micrometers.
 11. The method of claim 1, further comprising thesteps of: isolating the polymer; blending the isolated polymer with athermoplastic resin; and hot melt coating or coextruding the blend. 12.The method of claim 11, wherein the coating method comprises hot meltcoating and the coating thickness is in the range from about 0.01 toabout 2.5 micrometers.